The Galactic Center Source IRS 13E: a Star Cluster

Abstract

High spatial resolution, near-infrared observations of the Galactic Center source, close to Sgr A , known historically as IRS13, are presented. These observations include ground-based adaptive optics images in the H, K' and L bands, HST-NICMOS observations in filters between 1.1 and 2.2 µm, and spectroimaging data in the He I 2.06 µm line and the Brγ line. Analysis of all these data has made possible the resolution of the main component, IRS 13E, into a cluster of seven individual stars within a projected diameter of ∼ 0.5 (0.02 pc), and to build their SED. The main sources, 13E1, 13E2, 13E3 (a binary), and 13E4, are hot stars of different nature. 13E2 and 13E4 are emission line stars. The spectral type of the various members goes from O5I to WR, including dusty WRs like IRS 21 (Tanner et al. 2002). All these sources have a common westward proper motion. Two weaker sources, 13E5 and 13E6, are also detected within the compact cluster, with 13E5 proposed as another dusty WR and 13E6 as a O5V star. An extended halo seen around the cluster, part of the mini-spiral of dust is particularly enhanced in the L band. It is interpreted as a contribution of the scattered light from the inner cluster and the thermal emission from the dust. IRS 13E is proposed to be the remaining core of a massive, young star cluster which was disrupted in the vicinity of Sgr A , and hence, the possible source of the young stars in the central parsec, from the helium stars to the S stars.

Kinematic and structural analysis of the Minispiral in the Galactic Center from BEAR spectro-imagery

“…Bar. The map peaks sharply at the location of the GCIRS 13E compact star cluster (Maillard et al 2004), which seems to show that this object excites local material in the Bar, and thus must be either embedded in it, or very close to it. Thus, the coincidence between this bright spot and the northern end of the western edge of the Minicavity seems to be a projection effect, and not physical.…”

“…-two of the gas patches detected in both lines having a high [He ]/[Brγ] ratio are coincident with the helium star GCIRS 34W; -the Bar, which is the main feature with the highest line ratio, is close to the GCIRS 16 helium star cluster, and seems to contain the GCIRS 13E star cluster (Appendix A), which is made of several high-mass-loss-rate stars (Maillard et al 2004); -the Tip, the feature with the highest [He ]/[Brγ] ratio, seems to be interacting with a stellar wind, as evidenced by the Microcavity, and is on the same line of sight as the helium star GCIRS 9W; -the differences in the shape of the Northern Arm between the two spectral lines appear to come from the geometry of the UV field around the GCIRS 16 cluster.…”